Android Developers Blog

Uniforms variables in GLSL are crucial for passing data between the game code on the CPU and the shader program on the graphics card. Unfortunately, up until the availability of OpenGL ES 3.1, using uniforms required some preparation which made the workflow slightly more complicated and wasted time during loading.

Let us examine a simple vertex shader and see how OpenGL ES 3.1 allows us to improve it:

That pattern leads to having to call glGetUniformLocation for each uniform in every shader and keeping the handles or worse, calling glGetUniformLocation every frame.

Warning! Never call glGetUniformLocation every frame! Not only is it bad practice but it is slow and bad for your game’s performance. Always call it during initialization and save it somewhere in your code for use in the render loop.

This process is inefficient, it requires you to do more work and costs precious time and performance.

Also take into consideration that you might have multiple shaders with the same uniforms. It would be much better if your code was deterministic and the shader language allowed you to explicitly set the locations of your uniforms so you don’t need to query and manage access handles. This is now possible with Explicit Uniform Locations.

You can set the location for uniforms directly in the shader’s code. They are declared like this

layout(location = index) uniform type name;

For our example shader it would be:

layout(location = 0) uniform mat4 matWorldViewProjection;

This means you never need to use glGetUniformLocation again, resulting in simpler code, initialization process and saved CPU cycles.

This is how the example shader looks after the change. Changes are marked in bold:

This change is extremely simple and the improvements can be substantial, producing cleaner code, asset pipeline and improved performance. Be sure to make these changes If you are targeting OpenGL ES 3.1 or creating multiple APKs to support a wide range of devices.

To learn more about Explicit Uniform Locations check out the OpenGL wiki page for it which contains valuable information on different layouts and how arrays are represented.